Lens for a semiconductive device with a laser and a photodetector in a common container

ABSTRACT

A laser and photodetector are combined in a common package. This permits the photodetector to monitor the light intensity emitted by the laser. The laser and photodetector can be produced monolithically on a common chip to improve the accuracy of positioning of the various components. The device can be disposed within a common container having a window through which the emitted light passes. The window can be configured to have inside and outside surfaces that selectively reflect a portion of the light back to the photodetector while transmitting the remaining portion of the light through the window to a phototransmissive device, such as an optical fiber. The light reflected back to the photodetector can be focused in a predetermined pattern to cause the light to be accurately received by the photodetector and not fall on the laser.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to lasers and photodetectorsand, more particularly, to a single component having a container withinwhich the laser and photodetector are disposed and arranged to permitthe photodetector to receive reflected light from the laser.

2. Description of the Prior Art

Many different types of lasers are known to those skilled in the art.One type of laser, referred to as a vertical cavity surface emittinglaser, or VCSEL, emits light in a single direction through an uppersurface of the laser structure. Furthermore, many types ofphotodetectors are known to those skilled in the art. The photodetectorscan be photodiodes, phototransisitors or any other photosensitivecomponent. In certain applications, the emitted power from a laser mustbe monitored to determine whether the power of the emitted light exceedscertain predetermined threshold magnitudes. This monitoring function isused to avoid any possible danger from the emission of unacceptably highpower levels from the laser. The monitoring function is also necessaryin order to maintain required modulation rates and on/off extinctionratios.

An article titled "Surface-emitting Microlasers for Photonic Switchingand Interchip Connections", published in Optical Engineering, March1990, Volume 29 No. 3 by Jewell, Scherer, McCall, Olsson, Harbison andFlorez describes vertical cavity electrically pumped surface emittingmicrolasers which are formed on gallium arsenide substrates at densitiesgreater than two million per square centimeter. Two wafers were grownwith indium gallium arsenide active material composing three quantumwells, 80 angstroms thick, in one and a single quantum well 100angstroms thick in the other. Lasing was seen in devices as small as 1.5micrometers diameter with less than 0.05 micrometers cube activematerial. Single quantum well microlasers 5×5 micrometer square had roomtemperature current thresholds as low as 1.5 milliampere with 983nanometers output wavelength. Ten-by-ten micrometer square singlequantum well microlasers were modulated by a pseudorandom bit generatorat one Gb/s with less than 10⁻¹⁰ bit error rate. Pulsed output >170milliwatt was obtained from a 100 micrometer square device. The laseroutput passes through a nominally transparent substrate and out of itsback side, a configuration well suited for micro optic integration andphotonic switching and interchip connections.

In an article titled "Vertical-Cavity Surface-Emitting Laser Arrays" byMorgan and Hibbs-Brenner, which appeared in SPIE Volume 2398, pages65-93, on Feb. 6, 1995, the authors reviewed the state-of-the-artperformance of producible 850 nanometer current guided galliumarsenide/aluminum gallium arsenide top emitting vertical cavity surfaceemitting lasers and arrays. The paper focuses on the flexibility of thistechnology platform in demonstrating a variety of devices and arrays. A99.8 percent device yield across a three inch diameter metal organicvapor phase epitaxy grown wafer is demonstrated with this design. Recentprogress in device performance have and will enable advances in VCSELarray based technologies. Included in the paper are unique ways ofengineering lasing characteristics for single mode or incoherentemission. Array applications include one dimensional addressable arrays,particularly in the area of high speed optical data links.

In SPIE (Society of Photo-Optical Instrumentation Engineers) Volume 1562(1991), an article titled "Devices for Optical processing" by Morgan,Chirovsky, Focht, Guth, Asom, Leibenguth, Robinson, Lee and Jewellreports on batch processed, totally planar, vertical cavity top surfaceemitting gallium arsenide/aluminum gallium arsenide laser devices andarrays. Different size devices are studied experimentally. The articledescribes the measurement of continuous wave threshold currents as lowas 1.7 milliamperes and output powers greater than 3.7 milliwatts atroom temperature. The article also discusses interesting characteristicssuch as differential quantum efficiencies exceeding unity andmultitransverse mode behavior. An array having a 64 by 1 individuallyaccessed elements is characterized and shown to have uniform roomtemperature continuous wave operating characteristics in thresholdcurrents approximately equal to 2.1 milliamperes with a wavelength ofapproximately 849.4 nanometers and an output power of approximately 0.5milliwatts.

U.S. Pat. No. 5,115,442, which was issued to Lee et al on May 19, 1992,discloses a top emitting surface emitting laser structure. Lasers ofthis type depend upon emission through apertured top surface electrodes.Biasing current, accordingly peripheral to the laser is introduced,follows the path which comes to confluence within the active region toeffectively attain lasing threshold. The path is the consequence of aburied region of increasing resistance which encircles the laser at orabove the active region. The buried region is produced by ionimplantation-induced damage with ion energy magnitude and spectrumchosen to produce an appropriate resistance gradient integrated, as wellas discrete, laser are contemplated by the patent. U.S. Pat. No.5,115,442 is hereby explicitly incorporated by reference.

U.S. Pat. No. 5,031,187, which was issued to Orenstein et al on Jul. 9,1991, discloses a planar array of vertical cavity surface emittinglasers. The device comprises an active region having a quantum wellregion disposed between two Bragg reflector mirrors separated by awavelength of the emitting laser. A large area of the structure is grownon a substrate and then laterally defined by implanting conductingreducing ions into the upper mirror in areas around the lasers. Thereby,the laterally defined laser array remains planar. Such an array can bemade matrix addressable by growing the structure on a conducting layeroverlying an insulating substrate. After growth of the verticalstructure, an etch or further implantation divides the conducting layerinto strips forming bottom column electrodes. Top row electrodes aredeposited in the perpendicular direction over the laterally defined topmirror. U.S. Pat. No. 5,013,187 is hereby explicitly incorporated byreference.

In IEEE Photonics Technology Letters, volume 4, no. 4 (April 1993), anarticle titled "Transverse Mode Control of Vertical-CavityTop-Surface-Emitting Lasers" by Morgan, Guth, Focht, Asom, Kojima,Rogers and Callis discusses transverse mode characteristics and thecontrol for vertical cavity top surface emitting lasers. It alsodescribes a spatial filtering concept for the control of VCSELtransverse modes allowing the achievement of over 1.5 mW single TEMtransverse mode emission from continuous wave electrically excitedVCSEL's. It also shows that, without spatial filtering, L-I and V-Ikinks can be observed.

U.S. Pat. No. 5,245,622, which was issued to Jewell et al on Sep. 14,1993, describes a vertical cavity surface emitting laser withintra-cavity structures. The intra-cavity structures allow the verticalcavity surface emitting laser to achieve low series resistance, highpower efficiencies and TEM₀₀ mode radiation. In one embodiment of theinvention, a VCSEL comprises a laser cavity disposed between an upperand a lower mirror. The laser cavity comprises upper and lower spacerlayers sandwiching an active region. A stratified electrode forconducting electrical current to the active region is disposed betweenthe upper mirror and the upper spacer. The stratified electrodecomprises a plurality of alternating high and low doped layers forachieving low series resistance without increasing the opticalabsorption. The VCSEL further comprises a current aperture as a discshaped region formed in the stratified electrode for surpressing highermode radiation. The current aperture is formed by reducing oreliminating the conductivity of the annular surrounding regions. Inanother embodiment, a metal contact layer having an optical aperture isformed within the upper mirror of the VCSEL. The optical aperture blocksthe optical field in such a manner that it eliminates higher transversemode lasing. U.S. Pat. No. 5,245,622 is hereby explicitly incorporatedby reference.

U.S. Pat. No. 5,237,581, which was issued to Asada et al on Aug. 17,1993, describes a semiconductor multilayer reflector and a lightemitting device. The reflector includes a plurality of first quarterwavelength layers each having a high refractive index, a plurality ofsecond quarter wavelength layers each having a low refractive index andhigh concentration impurity doping regions. The first and second layersare piled up alternately and each of the doping regions is formed at aheterointerface between the first and second layers. In this structure,the width and height of the potential barrier at the heterointerfacebecomes small so that tunnel current flowing through the multilayerreflector is increased. U.S. Pat. No. 5,237,581 is hereby explicitlyincorporated by reference.

U.S. Pat. No. 5,258,990, which was issued to Olbright et al on Nov. 2,1993, describes a visible light surface emitting semiconductor laser.The laser comprises a laser cavity sandwiched between two distributedBragg reflectors. The laser cavity comprises a pair of spacer layerssurrounding one or more active, optically emitting quantum well layershaving a bandgap in the visible range which serves as the activeoptically emitting material of the device. The thickness of the lasercavity is defined as an integer multiplied by the wavelength and dividedby twice the effective index of refraction of the cavity. Electricalpumping of the laser is achieved by heavily doping the bottom mirror andsubstrate to one conductivity type and heavily doping regions of theupper mirror with the opposite conductivity type to form a diodestructure and applying a suitable voltage to the diode structure.Special embodiments of the invention for generating red, green and blueradiation are also described in this patent. U.S. Pat. No. 5,258,990 ishereby explicitly incorporated by reference.

U.S. Pat. No. 5,331,654, which was issued to Jewell et al on Jul. 19,1994, discloses a polarized surface emitting laser. It describes avertical cavity surface emitting semiconductor diode laser having amonolithic and planar surface and having lateral anisotropy in order tocontrol the polarization of the emitted light beam. The diode laserincludes a body of a semiconductor material having an active regiontherein which is adapted to generate radiation and emit the radiationfrom a surface of the body, and a separate reflecting mirror at oppositesides of the active region with at least one of the mirrors beingpartially transparent to the generated light to allow the lightgenerated in the active region to be emitted therethrough. Theanisotropy may be provided by utilizing anisotropy in the atomic ormolecular structure of the materials forming the laser or by anisotropicpatterning or deliberate offset alignment in processing of the laser orthrough anisotropic structures in the laser cavity to control thepolarization of the emitted beam. U.S. Pat. No. 5,331,654 is herebyexplicitly incorporated by reference.

U.S. Pat. No. 5,351,256, which was issued to Schneider et al on Sep. 27,1994, describes an electrically injected visible vertical cavity surfaceemitting laser diode. Visible laser light output from an electricallyinjected vertical cavity surface emitting laser diode is enabled by theaddition of phase matching spacer layers on either side of the activeregion to form the optical cavity. The spacer layers comprise indiumaluminum phosphide which act as charge carrier confinement means.Distributed Bragg reflector layers are formed on either side of theoptical cavity to act as mirrors. U.S. Pat. No. 5,351,256 is herebyexplicitly incorporated by reference.

U.S. Pat. No. 5,359,447, which was issued to Hahn et al on Oct. 25,1994, discloses an optical communication with vertical cavity surfaceemitting laser operating in multiple transverse modes. The communicationsystem uses a relatively large area vertical cavity surface emittinglaser. The laser has an opening larger than approximately 8 micrometersand is coupled to a multimode optical fiber. The laser is driven intomultiple transverse mode operation, which includes multiplefilamentation as well as operation in a single cavity. U.S. Pat. No.5,359,447 is hereby explicitly incorporated by reference.

In IEEE Photonics Technology Letters, Volume 7, No. 5 (May 1995), anarticle entitled "200° C., 96-nm Wavelength Range, Continuous-WaveLasing from Unbonded GaAs MOVPE-Grown Vertical Surface-Emitting Lasers"by Morgan, Hibb-Brenner, Marta, Walterson, Bounnak, Kalweit and Lehmandescribes record temperature and wavelength range that was attainedthrough the use of MOVPE-grown AlGaAs vertical cavity surface-emittinglasers. Unbonded continuous-wave lasing is achieved at temperatures upto 200° C. from these top-emitting VCSEL's and operation over 96-nmwavelength regime near 850 nm is also achieved from the same nominaldesign. Temperature and wavelength insensitive operation is alsodemonstrated in this article and the threshold current is controlled towithin a factor of 2 (2.5-5 mA) for a wavelength range exceeding 50 nmand to within 30 percent (5-10 mA) for a temperature range of 190° C. at870 nm.

It would be significantly beneficial if a laser could be manufactured insuch a way that a photodetector is disposed within a common containerwith the laser to receive reflected light and monitor the intensity ofthe laser's light emission.

SUMMARY OF THE INVENTION

A generally related invention is the subject of U.S. patent applicationSer. No. 08/687,701, commonly assigned.

The present invention discloses several embodiments that are intended tohelp solve the problem of producing a laser and a photodetector in acommon container wherein the photodetector can monitor light emittedfrom the laser and reflected by a window of the container. The presentinvention comprises both the structure that permits the laser andphotodetector to be manufactured for placement within a common containerand, furthermore, a method by which the light can be efficientlyreflected from a window of the container back toward the photodetector.

One embodiment of the present invention comprises a laser and aphotodetector, wherein the laser and the photodetector are disposed in acommon structure. The common structure can be a monolithicsemiconductive device on which the laser and photodetector are bothmanufactured concurrently and reside within a common semiconductor chip.Alternative embodiments could place a discrete laser on a previouslymanufactured photodetector to accomplish similar purposes.

In one embodiment of the present invention, the laser is a verticalcavity surface emitting laser, or VCSEL. The laser can comprise aplurality of layers which form a light emitting structure and thephotodetector can comprise a photosensitive layer disposed over thelight emitting structure. A portion of the photosensitive layer can beetched to form a cavity which exposes the light emitting structurebeneath the photosensitive layer of the photodetector. In certainarrangements, the cavity can be surrounded by the photosensitive layerto place the laser in the center of a photodetector structure.Alternatively, the laser and the photosensitive layer can be arranged ina side by side relationship. The common container in which both thephotodetector and the laser are disposed can be provided with a windowthat is partially reflective and partially transmissive. A portion ofthe light emitted by the laser is then reflected back toward thephotodetector.

One embodiment of the present invention provides a means for efficientlyreflecting the light from the laser back toward the photodetector. Thatembodiment of the present invention comprises a laser, a photodetectorand a container with a window. The laser and the photodetector aredisposed in a common structure within the container. The window ispartially reflective and partially transmissive and has an insidesurface facing the laser and the photodetector. The window also has anoutside surface facing away from the laser and the photodetector. Theinside surface is shaped to reflect light from the laser toward thephotodetector in a first predetermined pattern which avoids the laser.In other words, the reflected light from the inside surface of thewindow is directed toward regions of the photodetector but not towardthe laser. The outside surface of the window can be shaped to transmitand focus light from the laser in a second predetermined pattern. Thissecond predetermined pattern can concentrate the light from the laser ona light transmissive member, such as an optical fiber. The firstpredetermined pattern can be an annular shape that surrounds the laser.In a particularly preferred embodiment of the present invention, theinside and outside surfaces of the window cooperate to reflect a portionof the light back toward the photodetector in an annular pattern thatavoids the laser while transmitting the remaining portion of the lightin a focused beam through the window toward a light transmissive device,such as an optical fiber used in communications systems.

While the two primary embodiments of the present invention can be usedin conjunction with each other, they can also be implemented inapplications that do not require their combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully and completely understood froma reading of the Description of the Preferred Embodiment in conjunctionwith the drawings, in which:

FIG. 1 shows a sectional view during an initial step of the manufactureof the present invention;

FIGS. 2 and 3 show side and top views during a subsequent step of themanufacturing of the present invention;

FIGS. 4 and 5 show the subsequent step following the configurationsshown in FIGS. 2 and 3;

FIGS. 6 and 7 show side and top views following a subsequent step afterthe production of the devices shown in FIGS. 4 and 5;

FIG. 8 is a more detailed view of FIG. 6;

FIG. 9 is the same as FIG. 8 except with an additional dielectric layerdesigned to passivate the VCSEL and photodetector surfaces and minimizereflections at the surface of the photodiode;

FIGS. 10 and 11 show alternative applications of a window that ispartially reflective and partially transmissive;

FIGS. 12 and 13 show the inside and outside surfaces of the window;

FIG. 14 shows an alternative embodiment of the present invention; and

FIG. 15 shows the voltage versus current relationships for Schottkymetals and ohmic metals.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout the Description of the Preferred Embodiment, like componentswill be identified by like reference numerals and letters. Themanufacturer of a device which incorporates both a laser and aphotodetector requires several sequential steps to be performed. Thestructure of the present invention will be described in terms of thesequential steps used to manufacture it.

The structure shown in FIG. 1 is an intermediate structure produced byfirst providing a substrate S which can be gallium arsenide. A bottommirror BM is disposed on the substrate. The bottom mirror can be anN-type mirror and, as understood by those skilled in the art, wouldtypically comprise a plurality of individual layers of preselectedthickness and material composition to provide the desired reflectancefor a vertical cavity surface emitting laser. Above the bottom mirror BMis an active layer A on which a top mirror TM is disposed. As known tothose skilled in the art and as described in great detail in the citedpatents and papers described above, the structure of the top mirrortypically comprises a plurality of individual layers of the appropriatethickness and material composition to result in the desired amount ofreflectance and transmissiveness necessary to produce a vertical cavitysurface emitting laser. The top mirror TM can typically be made ofP-type conductivity material. A contact layer C is disposed on the topmirror and typically comprises highly doped P-type conductivitymaterial. An etch stop layer SE is disposed on the contact layer C andan undoped photodetector layer PD is disposed on the etch stop layer SE.

With continued reference to FIG. 1, the substrate S is made of galliumarsenide, the bottom mirror BM comprises alternating layers of aluminumarsenide and gallium aluminum arsenide. The active layer A provides thequantum well of the laser and also incorporates the confinement layersnecessary to confine the injected charge carriers to the quantum wellsin the laser. The active layer typically comprises one or more quantumwell made of gallium arsenide material and the confinement layerstypically comprise gallium aluminum arsenide. The top mirror TMcomprises a plurality of alternating layers of aluminum arsenide andgallium aluminum arsenide. The contact layer C is made of galliumarsenide material and the etch stopping layer SE is made of aluminumarsenide or gallium indium phosphide. The photodetecting layer PD ismade of gallium arsenide.

In a typical application of the present invention, the substrate S isapproximately 625 microns thick, the total thickness of the plurality ofstacks used to make the bottom mirror is approximately 4 microns thick,the active layer and confinement layers combine for a thickness ofapproximately 0.26 microns, and the plurality of layers used to providethe top mirror TM combined for a thickness of approximately 3 microns.The contact layer C is approximately 0.02 microns thick and the stopetch layer SE is approximately 0.02 microns thick. The photodetectorlayer PD is approximately 1 micron thick.

The structure shown in FIG. 1 illustrates an intermediate configurationof the present invention following the initial steps necessary toprovide the plurality of layers shown. The manufacturing method used toproduce the layers shown in FIG. 1 are well known to those skilled inthe art. For example, all layers can be deposited using metal-organicvapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE).

In FIGS. 2 and 3, side and top views are shown of the present inventionduring a subsequent step in the manufacturing process following theproduction of the intermediate device illustrated in FIG. 1. Twoseparate conductive members are disposed on the top surface of thephotodetector layer PD. As can be seen in FIG. 3, these conductors areassociated with each other to provide two generally concentric partialcircles which are each connected to an individual contact pad. The innercircle 10 is connected to contact pad 12 and the outer circle 14 isconnected to contact pad 16. Between these two concentric contactregions, a portion of the photodetective surface 20 is disposed. Itshould be understood that the entire surface in FIG. 3 on which theconductors, 10 and 14, are disposed is made of photosensitive materialto provide the photodetector layer PD. However, the two conductors, 10and 12, define a preselected portion 20 of the photosensitive materialbetween them. This arrangement forms a photodiode between contact pad 12and contact pad 16. As illustrated, FIG. 2 is a sectioned view of FIG. 3taken through the central portion of the circular conductors as shown.

With reference to FIGS. 4 and 5, a subsequent step in the manufacture ofthe present invention comprises the step of etching a cavity 30 which,as illustrated in FIG. 4, removes a portion of the photodetector layerPD and the etch stop layer SE to expose the structure below these layerswhich comprises the layers of the laser. As can be seen in FIG. 5, thecavity 30 is generally surrounded by the photodetector layer 20 thatlies between the two conductors, 10 and 14. Throughout this descriptionof the present invention, the arrangement shown in FIG. 5 will bereferred to as having the laser surrounded by the photodetector, but itshould be realized that the photodetector portion 20 between thecontacts, 10 and 14, does not totally surround the laser portion withinthe cavity 30. However, for purposes of simplicity, the arrangementshown in FIG. 5 will be described as having the laser surrounded by thephotodetector.

FIGS. 6 and 7 illustrate the side and top views of the device followinga subsequent manufacturing step. A gain guide implant 60 is produced bythe step of ion implantation of hydrogen ions at a single energy todeposit the ions at a given depth and an isolation implant 62 isprovided by the manufacturing step of ion implantation of hydrogen ionsat multiple energies to distribute the ions from the region of thebottom mirror BM up to the top contact. The gain guide implant 60 isgenerally annular in shape and the isolation implant 62 is generallycylindrical in shape. These two implants are generally concentric witheach other and with cavity 30. The function of the gain guide implant 60is to guide current through the center of the laser and the function ofthe isolation implant 62 is to isolate the laser from neighboringdevices. As can be seen, the gain guide implant is predominatelydisposed within the top mirror TM while the isolation implant extendsthrough the photodetector layer PD, the etch stop layer SE, the contactlayer C, the top mirror TM, the active layer A and part of the bottommirror BM. A P-type ohmic metal contact 70 is disposed on the exposedsurface of the contact layer C and shaped to extend to a contact pad 72.In addition, a back side N-type ohmic metal contact M is provided on thebottom surface of the structure shown in FIG. 6. The current flowingthrough the vertical cavity surface emitting laser will flow betweenohmic contact 70 and layer M. The conductor that extends between metalcontact 70 and contact pad 72 lies on both the upper surface of thephotodetector layer PD and the exposed upper surface of the contactlayer C within cavity 30. Therefore, it has a step formed in its length.

FIG. 8 is a more detailed illustration of the device shown in FIG. 6. Itshows the physical relationship between the gain guide implant 60 andthe isolation implant 62 with respect to the ohmic metal contacts 70within the cavity. Dashed box 80 illustrates the active region withinthe active layer A where lasing occurs. Light emitted from the activeregion passes upward through the top mirror TM and within the opening ofthe circular ohmic metal contact 70. Light received downward on thephotodetector region 20 between the two concentric conductors, 10 and14, creates a responsive conductance of the photodetector layer PD thatcan be sensed from an increase in current flow between the concentricconductors, 10 and 14.

FIG. 9 shows the representation illustrated in FIG. 8, but with an addeddielectric layer 90 disposed over the top of all of the upper surface ofthe device. The dielectric layer would typically have a thickness equalto one half the wavelength of the light emitted by the vertical cavitysurface emitting laser. The dielectric layer would typically be made ofsilicon dioxide or silicon nitride. It is provided for the purpose ofpassivating the surface and reducing reflections of incident light fromthe surface of the photodetector. Since the dielectric layer would havea constant thickness throughout its entire structure, it should be notedthat small perturbations would typically occur in the upper surface ofthe dielectric layer. However, these perturbations, where the uppersurface of the photodetective layer PD have the conductors, 10 and 14,disposed on it, are not shown in the Figures. In addition, it should beunderstood that many of the dimensions of the Figures have beenexaggerated for purpose of clarity and simplicity of illustration. Thevarious thicknessess of the layers and implant areas have beenexaggerated and are therefore not drawn to scale. For example, the innerdiameter of the ohmic metal contact 70 is approximately 15 microns andits outer diameter is approximately 35 microns. The inner diameter ofthe contact identified by reference numeral 14 is approximately 300microns and the outer diameter of the contact identified by referencenumeral 10 is approximately 125 microns.

In order to fully utilize the capability of the present invention, whichprovides both a laser and a photodetector in a common structure, thesemiconductive device described above would typically be disposed withina container that is provided with a window through which the light canpass after being emitted by the laser. FIG. 10 shows an exemplaryillustration of this type of structure. Reference numeral 100 is used inFIG. 10 to represent the total structure shown in FIG. 9 and describedabove. By dashed lines in FIG. 10, the photodetector regions 104 and thelaser portion 108 of the device 100 are schematically represented. Fromthe laser 108, emitted light EL passes toward a window 110. The window110 is provided with an inside surface 112 and an outside surface 114.As shown in FIG. 10, the inside surface 112 faces the laser 108 and thephotodetector 105. The outside surface 114 faces away from thesecomponents. The window 110 is partially reflective and partiallytransmissive. A portion of the emitted light EL from the laser 108 isreflected back toward the photodetector 104 as reflected light RL. Theremaining portion of the emitted light EL passes through the window 110as transmitted light TL. The reflected light RL is a uniform sample ofall of the light emitted from the laser. In other words, the windowreflects an equal percentage of the light incident on any part of thewindow. This prevents problems that could otherwise be associated withmodal noise. In a preferred embodiment of the present invention, theinside surface 112 of the window 110 is shaped to cause the reflectedlight RL to be focused in a first predetermined pattern. In aparticularly preferred embodiment of the present invention, the firstpreselected pattern is annular in shaped. The arrows in FIG. 10represent this annular shaped pattern. The emitted light EL from thelaser which is reflected back toward the photodetector 104 is directedback in such a way that it strikes the photodetector to provide anannular area of illumination that avoids the laser 108. In other words,the reflected light RL strikes the device 100 to illuminate an annularpattern on its surface that is generally coincident with the circularphotodetector 104. The laser 108 lies within the annular pattern andgenerally does not receive the reflected light RL. The transmitted lightTL passing through the window 110 is focused in a second predeterminedpattern that causes it to fall predominately on a light transmissiveobject such as optical fiber 120. By shaping the inside surface 112 andthe outside surface 114 of the window 110, the efficiency and accuracyof the device is significantly increased. Under certain circumstances,light reflected by the window 110 could otherwise fall on the laser oroutside the region of the photodetector. The selective reflectionprovided by the inside surface 112 of the window 110 avoids thesedeleterious and wasteful results and also improves the operation of thelaser. It is important, if the photodetector is used to monitor theoutput power of the laser, that the light received by the photodetectoris an accurate and consistent proportion of the light transmittedthrough the window 110. Otherwise, the monitoring ability of thephotodetector is severely jeopardized.

FIG. 11 is generally similar to FIG. 10, but with a slightly differentconfiguration regarding the photodetector 104 and laser 108. In FIG. 11,the laser 108 is a discrete component that is attached to thephotodetector 104 after the two individual subcomponents aremanufactured. The illustration in FIG. 11 shows a photodetector 104 anda discrete laser 108 that are not formed as part of a monolithicstructure.

FIGS. 12 and 13 show the inside surface 112 and the outside surface 114,respectively, of the window 110 described above in conjunction withFIGS. 10 and 11. The inside surface 112 of the window 110 is providedwith a plurality of concentric rings 122 that are shaped into the insidesurface to cause it to selectively reflect the light from the laser backtoward the photodetector in a first preselected pattern. Although manypreselected patterns could be implemented, a particularly preferredpattern reflects the light to concentrate it in an annular shape asdescribed above. This concentration of the light in an annular patternserves the purpose of avoiding the results described above wherein thelight can fall on the laser itself or outside the boundaries of thephotodetector. The outside surface 114 of the window 110 is shaped tofocus the transmitted light in a second predetermined pattern. Thesecond predetermined pattern concentrates the light on a lighttransmissive member, such as an optical fiber. These specific shapes ofthe concentric rings in FIGS. 12 and 13 are selected, according tooptical principles that are generally known to those skilled in the art,to satisfy the goals of reflecting light in the first preselectedpattern and transmitting light in the second preselected pattern. Thecombination of this particular reflectance pattern and particulartransmission pattern serves the purpose of improving the efficiency ofthe device shown in FIGS. 10 and 11 in two ways. First, it allows thedevice to more effectively monitor its own output power. Secondly, itimproves the light transmission of the device for more efficient use incommunications systems.

The inside surface 112 and the outside surface 114 each will consist ofa diffractive phase element that is specifically implemented for thetransformation or function intended for each of the surfaces. As is wellknown to those skilled in the art, a diffractive optic is an opticalelement that uses diffraction to control wavefronts. With regard to thepreferred embodiment of the present invention, the diffractive optic canbe any optical device which utilizes diffraction to transform a pointsource intensity distribution into another desired intensitydistribution, such as an annular ring or another point sourcedistribution. Typical examples of a diffractive optic are zone plates,volume holographic lenses, surface relief conform lenses, holographiclenses, binary optics, computed generated holograms, and diffractiongratings. Fabrication methods that are usable in the manufacture ofdiffractive optics include diamond machining, interference of coherentbeams, and several forms of advanced microlithographic and etchingtechniques. Diffractive optics may be manufactured in large quantitiesby several replication methods, such as injection molding, embossing,and replicative transfer.

With reference to FIGS. 12 and 13, it should be clearly understood thatthe actual phase contours of the inside surface 112 and outside surface114 will typically be much denser than illustrated in the Figures.However, the design and specification of the mathematical prescriptiondefining the diffractive element on each of the two surfaces is verywell known to those skilled in the art and familiar with modern opticaldesign tools and methods. The distribution and shape of the phasecontours typically specify the optical function embodied in thediffractive element and the surface profile, or blaze, specifies theefficiency with which light is directed into one diffraction order. Thelens used in conjunction with the preferred embodiment of the presentinvention involves the general principle that a diffractive element hasa high efficiency in reflection and has a low efficiency intransmission, or vice versa. The diffractive element on the innersurface 112 is designed to be efficient in the first order inreflection. The fraction of the incident light that is directed backinto the power monitor detector by the lens equals the product of theefficiency times the reflectance of the inner surface 112. A fraction,equivalent to one minus the reflectance, of the incident light istransmitted by the inner surface 112 to the outer surface 114. Becausethe inner diffractive element is very inefficient in transmission, mostof the transmitted light occurs in the zero diffractive order. In otherwords, approximately 80 percent of the transmitted light behaves as ifthe inner diffractive element is not present. The light transmitted inzero order is then affected by the diffractive element on the outersurface 114 to focus it. The diffractive element on the outer surface ismachined to have a high efficiency in transmission. The distribution oflight between reflected component and transmitted component can becontrolled and adjusted by deposition of a film of specified reflectanceon the innersurface. For purposes of safety and the prevention of damageto an operator's eyes, it may be advantageous to adjust the first orderefficiency of the diffractive element on the outer surface 114 to beless than maximum in order to cause some of the light to diverge inhigher orders at large angles, thus minimizing potential hazards to anobserver.

FIG. 14 shows an alternative embodiment of the present invention whichis configured in a slightly different arrangement than that describedabove in conjunction with FIGS. 3, 5 and 7. In the description of FIGS.3, 5 and 7, the laser and the photodetector were arranged concentricallywith the photodetector being disposed around the laser. This particulararrangement, although advantageous in many applications where monitoringof the output power from the laser is necessary, is not required in allembodiments of the present invention. For example, the photodetectorcould comprise two conductors shaped as shown in FIG. 14. A firstcontact pad 140 is connected to a conductor that is shaped to have aplurality of fingers, 141, 142 and 143. Another contact pad 150 isconnected to a conductor that is shaped to have a plurality of fingers,151, 152 and 153. The fingers of the two structures are arranged to bein noncontact association with each other and to define a region ofphotodetector surface 160 between them. The structure shown at the leftside of FIG. 14 would operate, as a photodiode, in a manner that isgenerally similar to the photodetector regions described above in thediscussion of the other preferred embodiment of the present invention.At the right side of FIG. 14, the ohmic conductor 70 is shown connectedto its contact pad 72. The central region 170 within the ohmic conductor70 is the area through which the light is emitted by the laser. Thepurpose of FIG. 14 is to show that the photodetector and the verticalvacity surface emitting laser can be provided monolithically withouthaving them arranged in a concentric pattern. In other words, themonolithic structure shown in FIG. 14 has a photodetecting region 174and a laser region 176, divided by line 180, that are not concentricwith each other. This allows the device to accommodate both transmitterand receiver channels on a semiconductor chip for parallel datacommunication links. Monolithic integration allows the device to matchthis semiconductor chip to a single fiber optical connector for bothtransmitting and receiving channels, thus resulting in a significantcost savings.

In the description of the present invention, reference is made toSchottky metals and ohmic metals. FIG. 15 illustrates the differencesbetween these two conductors. There are differences between Schottkymetals and ohmic metals in electrical characteristics and, occasionally,in their composition. The solid line 200 in FIG. 15 shows thecharacteristic behavior of an ohmic metal contact to a semiconductor. Asvoltage increases or decreases, the current through the contact changesaccordingly and in a generally linear relationship. A Schottky metalcontact, on the other hand, behaves in the manner illustrated by dashedline 202 in FIG. 15. Schottky metals are particularly designed not toreact metallurgical with semiconductor materials and form a planarinterface. An example would be a thin titanium layer, approximately 50to 200 angstroms thick on top of which any amount of gold contact can beprovided. An ohmic metal contact can be formed by doping thesemiconductor very heavily, as with 3×10¹⁹ carbon, zinc or beryllium percubic centimeter for P-type conductivity materials or 5×10¹⁸ silicon ortellurium per cubic centimeter for N-type conductivity material. Thecarriers are transferred easily to the semiconductor and any metal canbe used, even metals that are typically used as Schottky metals.Alternatively, an element is placed in the metal which will diffuse intothe semiconductor and dope it. For example, zinc in a gold/zinc contactwill dope P-type material into the semiconductor. As a third alternativefor forming an ohmic contact, a metal is deposited which will form athird compound with a semiconductor, wherein this intermediate compoundallows easy current flow. For example, nickel-germanium-gold will reactwith gallium arsenide to form an intermediate nickel-germanium-galliumcompound. With reference to FIG. 7, the conductors identified byreference numerals 10, 14, 12 and 16 are Schottky metals. The metalsidentified by reference numeral 70 and 72 are ohmic metals.

The present invention, in a particularly preferred embodiment, relatesto a monolithic integration of a vertical cavity surface emitting laserand a photodetector which can be arranged as single pairs or arrays.Each pair can be arranged in a side by side configuration orconcentrically. These arrangements allow the photodetector to monitorthe output power of the VCSEL or, alternatively, reduce connector costsby providing a precise spacing between photodetectors and VCSEL's. In adevice made in accordance with the present invention, an epitaxialgrowth involves the deposition of the layers required for the VCSEL,followed by the layers required for the photodetector. For a VCSEL, anN-type layer is grown first and then the active region followed by theP-type mirror. An aluminum arsenide stop etch layer SE, which isapproximately 100 nanometers thick, is then grown, followed by anundoped gallium arsenide photodetector layer PD, which is approximately1 micrometer thick. The gallium arsenide photodetector PD serves as theabsorption layer for the photodetector. This process can then befollowed by additional layers which can be used for the fabrication offield effect transistors. For instance, the capability withcomplementary heterostructure field effect transistor (CHFET)technology, additional channel, barrier and contact layers would bedeposited. The processing of the VCSEL would involve a selective etch toremove the layers above the VCSEL, including the thick gallium arsenidephotodetector layer PD. Then the aluminum arsenide stop etch layer SEwould also be removed. At this point during the manufacturing process,standard VCSEL processing steps would be followed, including depositionof the top P-type ohmic contact layer, gain guide implant and theisolation implant, and the deposition of the metal on the back side ofthe wafer. The photodetector fabrication would then involve thedeposition of Schottky metal in the case of a metal-semiconductor-metal,or MSM, detector or deposition of ohmic metals and ion implantation inthe case of a photoconducting or pin detector. The ability to usephotolithography and wafer level processing allows the photodetector tobe located very accurately with respect to the laser to achieve accuracyof one micrometer or better. This may also result in reduced costs dueto the reduction in wafer area required and elimination of separatepackaging and processing steps. The integrated chips can also becombined with packaging approaches to address the need for monitoringthe output of a laser diode for data communication applications asdescribed above. Separate photodetectors would be used for the laseroutput monitoring function and for data communications channels. Theintegrated chip can also be applied in such a way as to reduce packagingcosts. Again, since the distance between the photodetector and the VCSELis very well known, array connector techniques can be used to create aconnector which brings an optical fiber to both the VCSEL and thephotodetector simultaneously. This procedure can be extended to arraysso that all channels, both ingoing and outgoing, are combined into asingle connector and receptacle. This approach can reduce chip,receptacle and connector costs.

Although the present invention has been described with particular detailand illustrated with significant specificity, it should be understoodthat alternative embodiments of the present invention are also withinits scope.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:
 1. A semiconductive device,comprising:a laser; a photodetector, said laser and said photodetectordisposed in a common structure; a container, said laser and saidphotodetector being disposed within said container; a window attached tosaid container, said window being partially reflective and partiallytransmissive, said window having an inside surface facing said laser andsaid photodetector, said window having an outside surface facing awayfrom said laser and said photodetector, said inside surface being shapedto reflect light from said laser toward said photodetector in a firstpredetermined pattern which avoids said laser, and said laser comprisesa plurality of layers which form a light emitting structure; and saidphotodetector comprises a photosensitive layer disposed over said lightemitting structure, a portion of said photosensitive layer being etchedto form a cavity which exposes said light emitting structure.
 2. Thedevice of claim 1, wherein:said outside surface is shaped to focus lightfrom said laser in a second predetermined pattern.
 3. The device ofclaim 2, wherein:said second predetermined pattern concentrates saidlight from said laser on a light transmissive member.
 4. The device ofclaim 3, wherein:said light transmissive member is an optical fiber. 5.The device of claim 1, wherein:said first predetermined pattern is anannular shape surrounding said laser.
 6. The device of claim 1, furthercomprising:said laser is a vertical cavity surface emitting laser. 7.The device of claim 1, wherein:said laser and said photodetector areformed on a common substrate.
 8. The device of claim 1, wherein:saidcavity is surrounded by said photosensitive layer.
 9. The device ofclaim 1, wherein:said laser and said photosensitive layer are arrangedin a side by side relationship.
 10. A semiconductive device,comprising:a laser; a photodetector, said laser and said photodetectordisposed in a common structure; a container, said laser and saidphotodetector being disposed within said container; and a windowattached to said container, said window being partially reflective andpartially transmissive, said window having an inside surface facing saidlaser and said photodetector, said window having an outside surfacefacing away from said laser and said photodetector, said inside surfacebeing shaped to reflect light from said laser toward said photodetectorin a first predetermined pattern which avoids said laser, said laserbeing a vertical cavity surface emitting laser, and said laser comprisesa plurality of layers which form a light emitting structure; and saidphotodetector comprises a photosensitive layer disposed over said lightemitting structure, a portion of said photosensitive layer being etchedto form a cavity which exposes said light emitting structure.
 11. Thedevice of claim 10, wherein:said outside surface is shaped to focuslight from said laser in a second predetermined pattern.
 12. The deviceof claim 11, wherein:said second predetermined pattern concentrates saidlight from said laser on a light transmissive member.
 13. The device ofclaim 12, wherein:said light transmissive member is an optical fiber.14. The device of claim 10, wherein:said first predetermined pattern isan annular shape surrounding said laser.
 15. The device of claim 10,wherein:said laser and said photodetector are formed on a commonsubstrate.
 16. The device of claim 10, wherein:said cavity is surroundedby said photosensitive layer.
 17. The device of claim 10, wherein:saidlaser and said photosensitive layer are arranged in a side by siderelationship.
 18. A semiconductive device, comprising:a laser; aphotodetector, said laser and said photodetector disposed in a commonstructure; a container, said laser and said photodetector being disposedwithin said container; and a window attached to said container, saidwindow being partially reflective and partially transmissive, saidwindow having an inside surface facing said laser and saidphotodetector, said window having an outside surface facing away fromsaid laser and said photodetector, said inside surface being shaped toreflect light from said laser toward said photodetector in a firstpredetermined pattern which avoids said laser, said laser being avertical cavity surface emitting laser, said outside surface beingshaped to focus light from said laser in a second predetermined pattern,said second predetermined pattern concentrating said light from saidlaser on a light transmissive member, said first predetermined patternbeing an annular shape surrounding said laser, said laser and saidphotodetector being formed on a common substrate; said laser comprisinga plurality of layers which form a light emitting structure, saidphotodetector comprising a photosensitive layer disposed over said lightemitting structure, a portion of said photosensitive layer being etchedto form a cavity which exposes said light emitting structure, saidcavity being surrounded by said photosensitive layer.